44 national geographic • August 2016
The potential for CRISPR research to
improve human medicine would be hard to over-
state. The technology has already transformed
cancer research by making it easier to engineer
tumor cells in the laboratory, then test various
drugs to see which can stop them from grow-
ing. Soon doctors may be able to use CRISPR to
treat some diseases directly.
Stem cells taken from people with hemo-
philia, for example, could be edited outside of
the body to correct the genetic flaw that causes
the disease, and then the normal cells could be
inserted to repopulate a patient’s bloodstream.
In the next two years we may see an even
more dramatic medical advance. There are
120,000 Americans on waiting lists to receive
organ transplants, and there will never be
enough for all of them. Thousands of people
die every year before reaching the top of the
list. Hundreds of thousands never even meet
the criteria to be placed on the list.
For years, scientists have searched for a way
to use animal organs to ease the donor shortage.
Pigs have long been considered the mammal of
choice, in part because their organs are similar
in size to ours. But a pig ’s genome is riddled with
viruses called PERVs (porcine endogenous ret-
roviruses), which are similar to the virus that
causes AIDS and have been shown to be capable
of infecting human cells. No regulatory agency
would permit transplants with infected organs.
And until recently, nobody has been able to rid
the pig of its retroviruses.
Now, by using CRISPR to edit the genome in
pig organs, researchers seem well on their way
to solving that problem. A group led by George
Church, a professor at Harvard Medical School
and MIT, used the tool to remove all 62 occur-
rences of PERV genes from a pig’s kidney cell. It
was the first time that so many cellular changes
had been orchestrated into a genome at once.
When the scientists mixed those edited cells
with human cells in a laboratory, none of the
human cells became infected. The team also
modified, in another set of pig cells, 20 genes
that are known to cause reactions in the human
immune system. That too would be a critical
mate in nature. But scientists hope that using
CRISPR to alter DNA could appease the oppo-
sition. It gives researchers the ability to rede-
sign specific genes without having to introduce
DNA from another species.
Golden rice, for example, is a GMO engi-
neered to contain genes necessary to produce
vitamin A in the edible part of the grain—
something that doesn’t happen naturally in rice
plants. Each year up to half a million children in
the developing world go blind for lack of vita-
min A—but anti- GMO activists have interfered
with research and prevented any commercial
production of the rice. With CRISPR, scientists
could almost certainly achieve the same result
simply by altering genes that are already active
in rice plants.
Scientists in Japan have used CRISPR to ex-
tend the life of tomatoes by turning off genes
that control ripening. By deleting all three cop-
ies of one wheat gene, Caixia Gao and her team
at the Chinese Academy of Sciences in Beijing
have created a strain that is resistant to pow-
dery mildew.
Farmers have been adjusting genes in single
species—by crossbreeding them—for thousands
of years. CRISPR simply offers a more precise
way to do the same thing. In some countries,
including Germany, Sweden, and Argentina,
regulators have made a distinction between
GMOs and editing with tools such as CRISPR.
There have been signs that the U.S. Food and
Drug Administration might follow suit, which
could make CRISPR-created products more
readily available and easily regulated than any
other form of genetically modified food or drug.
Whether the public will take advantage of them
remains to be seen.
Without regulation,
the tremendous
potential of this
revolution could be
overshadowed by fear.